Internegatives are used in producing high quality color prints from transparencies. For example, an enlarger may be used to project an image from a 35 mm color transparency through selected color filters and onto a 8.times.10-inch internegative and, after developing the internegative, a contact print or enlargement may be made therefrom. The results obtained are dependent, in part, upon the filtration given to the internegative as well as subsequent color adjustments of color filters used to make the color print or enlargement. Resulting color is also dependent, in part, upon the color response characteristics of internegatives which are variable, being affected by variations in the conditions of storage and handling to which the internegatives have been subjected and also by variations in the materials and processes used in manufacture of the internegatives. In an attempt to compensate for such variations, frequent tests are mandatory and various color balancing methods have been used.
The aim is to secure a good neutral scale on the final color print, showing a wide range of neutrals from light tone values to darkest values. The standard recommendation is that empirical methods of testing be performed by exposing through silver gray scale tablets. Using conventional methods, the testing may consume days of experiment and laborious readings of internegative steps through red, green and blue filters. In a plot method, such readings are plotted on graph paper to see if all three color readings "track together" and to see that no "humps" occur in center scale.
Nearly two hours is required for developing an internegative and making a color print therefrom and a number of exposures are oftentimes necessary, especially when the filtration values initially selected are quite different from the optimum values. Making a print may not be necessary if a VCNA (Video Color Negative Analyzer) is available to be used to directly analyze an internegative. However, a considerable amount of time must still be spent since developing of an internegative may require an hour or more and in many cases a print will be required even when a VCNA is available.
Standard gray scales used in the empirical methods are black-and-white silver images in the form of a series of eleven or twenty-one contiguous rectangular "steps" of progressively different densities. In the eleven-step gray scale, the density difference between consecutive steps is 0.30 which is equivalent to 0.30 log E or one lens step. In the twenty-one step gray scale, the density difference between consecutive steps is 0.15.
In a plot method as aforementioned, the red, green and blue densities of the reproduced steps may be measured and plotted to produce curves for comparison with empirical data set forth in standard curves to determine what changes in color filtration may be required. In an alternative two-point procedure, which is less accurate but which requires less time, the color densities of two steps are measured and the differences therebetween are determined. Then filter changes and exposure changes are determined from reference to empirical data in look-up tables. Another method is similar to the plot method but uses a computer and a gray scale having an emulsion similar to that of the film to be balanced. The computer is programmed for entry of data from densitometer readings and compares such data with stored empirical data to compute recommended filtration data, the entered and computed data being stored for future reference.
These methods require that the photographer spend a considerable amount of time in carrying out densitometer measurements and other specified procedures and there is a possibility for measuring, entry, computational or other error. Even without any such errors, the results obtained are not reliable. The recommended procedures can be carried out with meticulous care, but it will be found that more often than not, the final prints obtained will not be entirely satisfactory and that it is necessary to take the time required for repeat procedures and make one or more changes in the filtration values if truly high quality prints are to be obtained.
The difficulties with the prior art methods are indicated by consideration of information pamphlets supplied by Eastman Kodak Company, describing in detail the laborious procedures necessary for performance of the methods. The pamphlet recommends that after obtaining the best color balance possible with an empirical method as described, the photographer should "Select a good transparency with visually sensitive areas such as flesh or concrete and neutral objects with a wide range of densities. Make the best print possible from this internegative. In this case, it is recommended that you make your final judgment from the scene content rather than the reproduction of the step tablet. Often, the best print for flesh will produce a slightly cyan or blue reproduction of the silver step tablet." (underlined portion in italics in original)
These problems with the prior art methods are exacerbated by the fact that the color balancing procedures should always be repeated when internegatives are to be used which are not from the same batch as manufactured and should also be repeated periodically even when from the same batch, since the characteristics of the film as well as processing can change with time. One result is that low quality products are frequently passed as being acceptable in order to avoid the time, expense and frustrations of trying to produce a high quality product.